Getting to grips with gases

A good understanding of the particulate nature of matter is essential for any student to grasp complex topics including entropy, equilibria and kinetics. Although primary school pupils typically learn about the behaviour of particles in different states of matter, with further reinforcement at 11-14 level, many able students still show poor understanding which inhibits progress at post-16 level.

Chiu and colleagues investigated students' understanding of the behaviour of particles in gases, and compared the results with teachers' predictions. The research centred on a computerised test which included dynamic elements which reveal characteristics of gas particles in some questions, allowing students to then select which representation most closely matched their own perception.

Students generally held one of three mental models: a) the weight model, where heavier particles tend to sink to the bottom of a container b) the size model, where larger particles push their way towards smaller ones (rather than vice versa) and c) the correct scientific model where particles become randomly distributed regardless of size and weight. The test examined whether or not students changed the model they applied when the orientation of the apparatus or the pressure was changed.

The study included reasonable sample sizes of 102 8th graders and 92 9th graders. Only a small percentage of students answered all questions correctly, and the 9th graders outperformed the 8th graders, as one might have expected. Interestingly, the teachers involved in the study made incorrect predications regarding students' answers, illustrating another impediment to teaching and learning in this area.The key finding is that the main misconception centres on a lack of knowledge of the random distribution of gas particles, which is in line with previous studies. The authors suggest that static images in textbooks may play a role in reinforcing this problem.

In their conclusions, the authors recommend that teachers identify their students' misconceptions more effectively to identify appropriate strategies, including the use of dynamic visual resources, to support progress.